Loud-speaker



M; c. HOPKINS LOUDv S EEEEE R um` 10,- 1930. M. c. HOPKINS 1,763,049

LOUD SPEAKER FiledF-eb, 1151926 sheets-'sheer s NVENTOR MARcuscHoPKlNs .v I I 1 fm' am y' u K l ATTORNEYS Patented June 1o, 1930 e UNITED STATES PATENT OFFICE MARCUS C. HOPKINS, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO HOP- KINS CORPORATION, OF JERSEY CITY, WARE NEW JERSEY, A CORPORATION OF DELA- LOUD- SPEAKER Applicationled February 11, 1926. Serial N o. 87,491.

'10 phra m. The connection between the central iaphragm and the external resonator or sound board is such that the central diahragm will respond to the relatively high r uencies and will efliciently reproduce the hig tones or sounds, and the relatively low frequencies will be transmitted through said connection to the sound board so that it will respond to the relatively low frequencies and will efficiently reproduce them. The principal object of this invention is to provide a loud speakerof the foregoing type, the sound board of which is made of synthetic lumber, and by this term I intend to include products of the type of relatively rigid sheets or boards made from libres that have been separated, in part, at least,'and then reassembled in heter-r ogeneous arrangement in a new assembly.

Synthetic lumber has the requisite properties for promoting the regeneration of the relatively low frequencies which are passed on to the sound board or resonator for reproduction. I am not prepared to state exactly what properties of synthetic lumber are responsi le for the improved operation of the loud speaker disclosed in this application, but undoubtedly the soft and porous nature of this material and its extreme lightness are contributing factors, and I attach particular importance to the fact that the material is free from grain and has its component fibres and groups of fibres in heterogeneous arrangement.

Several forms of loud speakers in which synthetic lumber may be advantageously employed are disclosed in the accompanying rawings, in which y Fig. 1 is a front view of a loud speaker especially designed for use in hotels, theatres, concert halls and similar places where a 50 large volume of sound is desired;

Fig. 2 is a side elevation of the speaker shown in Fig. l;

Fig. 3 is a rear view of the loud speaker shown in Fig. l;

Fig. 4 is a vertical sect-ion taken on the line 4-4 of Fig. 3;

Fig. 5 is an enlarged detail vertical section of the central portion of the loud speaker showing the connection between the central diaphragm and the external sound board or resonator.

Fig. 6 is a front elevation of another type of loud speaker operating on the same principle as that shown in Fig. 1;

Fig. 7 is a top plan view of the loud speaker shown in Fig. 6;

*.Fig. 8 is a rear elevation of the speaker shown in Fig. 6; Y

Fig. 9 is a vertical 9 9 of Fig. 8;

Referring first to Figs. 1 to 5 inclusive, the loud speaker shown in these figures comprises a central conical diaphragm or tympanum 1 coupled to a vibratory resonator or sound board 2 by means of a semi-flexible coupling,

section taken on the line shown in Fig. 5. The conical diaphragm 1 formed, the paper is creased and then folded up to form a forwardly flaring brim 3 (Fig. 5). This brim naturally assumes an angle to the plane of the base equal to the anglebetween the radial elements of the cone and that base. The outer edge portion of the brim 3 is preferably glued to the inner circular edge of the resonator or sound board 2. For this purpose the inner circular edge of the sound board is tapered as shown at 4 and the outer edge portion of the brim 3 seats upon and is glued tothe `tapering surface thus formed. In gluing or cementing the brim to the beveled edge 4 it is important that a part of the brim be left free to form a hinge on which the cone may float. Thus with a brim 3/4 wide the cemented portion may have a width of 1A of an inch more or less and the remainder of the brim may be left free to swing.

The resonator or sound board 2in accordance with this invention, is made of synthetic lumber.

The vibratory actuating force is applied to the apex of the conical diaphragm by means of a rod or Wire 5 vvhich is adapted to be maintained in fixed relation with the diaphragm by means of a set screw 6. The rod 5 may be actuated by electromagnetic mechanism housed in the casing T. The casing 7 may be attached to a support or spider 8 which in turn may be aflixed to the resonator or sound boa'rd by means of Wood screws 9.

Il hile the loud speaker shown in Figs. 1 to 5 inclusive may be made of any desired size within reasonable limits, it has been found that for concert Work excellent results' have been obtained by making the conical diaphragm approximately 17 inches in outside diameter and the resonator or sound board approximately -l feet in outside diameter. The relatively large size of the loud speaker shoivn in Figs. 1 to 5 inclusive makes it desirable to suspend it by cords or chains which may be attached to any suitable part of the loud speaker, preferably the spiderA 8. The loud speaker may be suspended from the ceiling of a room, a bracket or any other supporting device.

The loud speaker shown in Figs. 6 to 9 inclusive is very similar in construction to that above described. It comprises a conical tympanum 1, a sounding board or resonator 2. a spider 8', for supporting the casing 7 of the electromagnetic actuating mechanism, and a forwardly Haring brim 3' on the cone which is attached to the inner edge of the sound board in the same manner as explained in connection with Figs. 1 to 5. The resonator or sound board 2 of this form of loud speaker is also made of s vnethetic lumber as in the case of the loud speaker described above. The main difference between the speaker shown in Figs. 6 to 9 inclusive and that shown in the first five figures is that the sound board or resonator 2 is of smaller diameter. The conical diaphragm 1 may or may not be smaller than the. conical diaphragm of the loudspeaker of figures l to 5. The reduction in overall size of the loud speaker shown in Figs. 6 to 9 inclusive makes it possible to support the speaker on a table or other horizontal surface and for this reason the sound board 2 is provided with suitable legs or cross pieces 1l) glued or otherwise fastened to the sound board. The sound board may be provided with an opening 11 to provide a hand grip for moving the loud speaker from one place to another. In constructing a loud speaker of the type shown in Figs. 6 to 9, I have found that excellent results are obtained by making the cone 2 approximately 151/2 in diameter and the sound board approximately 22 in diameter. This makes the transverse width of the annular sound board approximately 31/2 but good results may be obtained by making the sound board of even less Width than this or of even Greater Width than the sound board shown in Figs. 1 to 5 inelusive.

In both types of speaker the central conical diaphragm efficiently reproduces the higher tones and perhaps some of the intermediate tones While the surrounding annular resonator or sound board efficiently reproduces the lower or bass notes. By reason of the fact that the sound board is made of synthetic lumber the reproduction of the lower or bass notes is very true'and faithful. The lower notes are not only accurately. reproduced but the tonal quality is excellent, t-he reproduction being soft and mellow.

vIn a loud speaker constructed in accordance with the foregoing description, the regenerated or reproduced sound Waves are substantially directly proportional both quantitatively and qualitatively to the actuating force and the sound so reproduced retains substantially the same balance of high and low tones as the original sound from which the actuating force Was derived.

In a companion application Serial No. 7 9,- 329, filed January 5, 1926, I have described and claimed a loud speaker having a sounding board made of balsa Wood. Loud speakers thus equipped give wonderfully accurate sound reproduction with good tonal quality and balance, but the sound boards are difficult to make, particularly if built up as a multipleply veneer. Balsa Wood splinters and breaks in the ply cutting machines and the cut pieces fray at the edges during handlinor in the mill.

Also the completed board is inclined to Warp unless special expedients are resorted to for holding it in shape.

By my present invention there is substituted a sound board material easily obtainable in the open market at low cost and having many of the advantages of balsa Wood Without its disadvantages.

One suitable material is made from bagasse and other fibrous material by separating the fibres of the raw material and then reassembling them in a felted, heterogeneous arrangement either With or Without the addition of a binder. The material as purchased is relatively light in weight and has an open porous texture with fibres and bundles of fibres of considerable length. These are characteristics which I have found desirable in the sound board of an electrically actuated loud speaker.

y Another suitable material is made from Wood by physically separating the fibres and then, after physical or other treatment, reassembling them in heterogeneous felted arrangement of a relatively rigid nature and of a porous texture as described in United States length in United States' Patents No.' 1,153,512

and No. 1,187,476.

These three materials are typical ofthat class of materials which I have chosen to call synthetic lumber. That of yPatents Nos. 1,153,512 and 1,187 ,47 6 is the best for eneral use, but very brilliant results may had from using the material of Patents Nos.l

1,631,171,1,631,172, and 1,631,173. The results with the first mentioned material are acceptable, but the material seems to lack either a stiffness in the individual fibres or a lack of secure attachment between one fibre' and its fellows where theycross one lanother in` their heterogeneous' arrangement. vIndividually the fibres should be stiff, and collectively they should rigidly interlock 4to form a orous'rigid mass; Just why that is, I do not know.

I claim f v 1. A loud speaker tympanum having a portion 'which is substantiallyffully responsive to the higher frequencies and a portion consisting essentiall of synthetic lumber which is substantially ully responsive to the lower frequencies. 0

2. 4A loud speaker tympanum hav1ng).a sound reproducingrim4 of synthetic lum er which is substantially fully responsive to the lower frequencies and aportion Within sa1d rim which is substantially` fully responsive to the higher frequencies.

3. A loud speaker tympanum of the cone type having a'sound reproducing rim which is substantially fully responsive to the lower frequencies and consisting essentially of .Wood fiber reassembled in heterogeneous arrangement.

.4. A loud s eaker comprising a relatively light and stiff) diaphragm, an external synthetic lumber sound board of greater mass than the diaphragm, anda flexible coupling between the two adapted to permitthe diaA phragm to respond to relatively high frequencies and `adapted to transmit the relatively low frequencies to the sound board.

5.' A loud speaker comprising a central relatively light and stiff diaphragm, an ex-` ternal synthetic lumber sound board of greater mass than the dia hragm, and a flexible coupling between t e two adapted to permit the central diaphragm to respond to relatively high frequencies and adapted to transmit the relatively low frequenciesto thesound board.

6. A loud speaker comprising a central confV ical diaphragm, an external synthetic lumber sound board of greater mass than the diaphragm, and a flexible coupling between the two adapted to permit the conical diaphragm to respond to relatively high frequencies and adapted to transmit the relatively low frequencies to the sound board.

7. A loud speaker comprising-a central conical diaphragm, an external synthetic lu\inber ating sound board and a connection between the conical diaphra and the sound board adapted to perm1t the central diaphragm to respond to relatively high frequencies and adapted to transmit the relatively low frequencies to the sound board.

8. A loud speaker comprising a central conical diaphra m,a synthetic lumber sound board provi ing an annular flange or skirt extendmg radially beyond the conical diahragm and a connection between theconical iaphr and the sound board adapted to permit t e conical diaphragm to respond to relativelyhigh frequencies and adapted to transmit the relatively low frequencies to the soundb'oard.

9. Aloud speaker comprising a central conical dia `hragm having an integral forwardly thetic lumber sound board providing-a flange portion extending radially beyondthe conical diaphragm, said hinge portion being `secured to said sound board. j

11. A loud speaker comprising a synthetic lumber sound board,'and a conical diaphragm flexibly connected thereto so that ak portion of the sound board extends radially beyond the conical diaphragm, the flexible connection between the conical diaphragm and the sound board being adapted to permit the conical diaphragm to respond to relatively high frequencies and being adapted to transmit the relatively low frequencies to the sound board.

12. A loud speaker comprising a central conical diaphragm made of paper, an eX- ternal sound board made of wood fibre reassembled in heterogeneous arrangement and a flexible connection between the two adapted .to permit the conical diaphragm to respond 13. A loud speaker comprising a synthetic lumber sound board having a central opening, a conical diaphragm mounted in said opening, actuating means for the conical diaphragm, and means for supporting said actu- 'means comprising a support attached to the sound board and spanning the central opening thereof.

14. `-Aloud speaker comprising an annular flat synthetic lumber sound board having a' circular central opening, a conical diaphragm having a circular periphery, said conicaldiaphragm being mounted in said opening, and a flexible cou ling between the conical diaphragm and tile lsound board adapted to permit the conical diaphragm to respond to relativelv high frequencies and adapted to transmit relativelvv loiv frequencies to the sound board.

15. A loud speaker comprising an annular synthetic lumber sound board having a central opening the edge port-ion of which is provided with a tapering seat, and a conical diaphragm mounted in said opening said diaphragm having a forwardly flaring frusto-conical brim portion secured to the sound board on said tapering seat.

16. A loud speaker comprising a flat annular sound hoard made of Wood fibre reassembled in heterogeneous arrangement, said sound board having a central opening the edge portion of which is provided with a tapering seat. and a. fibrous conical diaphragm mounted in said opening and having an integral forwardly projecting brim portion, a partJ of said brim portion being attached to the Sound board at said tapering seat.

In testimony whereof I affix my signature.

MARCUS C. HOPKINS. 

